1. Field of the Invention
This invention relates to an apparatus and a method for processing images-that are applicable to copying machines, image scanners for scanning images on an original and even to host computers directed to image processing.
2. Related Background Art
Conventionally, any papers that should be protected from duplication, such as secret documents, have been labelled with a stamp clearly showing no copying. Alternatively, the papers have been printed with an indication that no part of it should be reproduced. Such stamp and indication can catch people""s attention but will not be sufficient protection against abused copying or counterfeiting.
In this respect, various methods have been proposed to print a particular stamp on an original as a xe2x80x9cspecific original discriminating patternxe2x80x9d, allowing interruption of copying operation in response to detection of this specific original discriminating pattern during scanning or so on.
There are, however, many disadvantages in the method relying on a particular stamp printed as the specific original discrimination pattern. First, an original may be excluded from the object to be copied if it contains by accident the same pattern as the particular stamp, which otherwise can be copied normally.
Second, the protection against copying requires that the specific original discriminating pattern is clear. Thus, the original with the specific original discrimination pattern can be copied when the pattern is printed at a limited area on the original and covered with something such as a seal.
In recent years, copying machines have been improved to reproduce a color image of higher quality as close as an original one. Such improvement results in an increased chance for the copying machine to be abused to counterfeit banknotes or valuable securities. With respect to these, various systems have been developed. For example, a seal impression on the banknote is detected to discriminate genuine banknotes or the like from the counterfeit ones.
In addition, the present applicant has proposed a system for discriminating the banknotes or the like by according to the specific tint unique for the original. This method is based on a fact that the banknotes or valuable securities have patterns printed thereon with inks of limited tints.
However, such feature recognition of the pattern cannot be a counter-measurement against the abuse of a copying machine because a tremendously huge amount of printed matter is and will be in circulation. Besides, a visible pattern used as the discriminating pattern stands out, which spoils the appearance of the printed matter itself.
This has necessitated development of a method of forming a pattern that is less visible or invisible to the naked eyes but can be detected by a device with a high accuracy.
To this end, the present applicant has proposed to print the specific mark with an ink having an infrared absorption characteristic. A device designed to detect such infrared is disclosed in Japanese Patent Application No. 4-286350 which comprises a reading sensor for infrared detection along with a reading sensor that is similar to those provided in typical devices for reproducing color images. These sensors share a common optical system to reduce the dimension of the entire apparatus. Optical adjustability of the apparatus has also been improved by using the single optical system as compared with an apparatus having two or more optical systems for individual sensors.
Various materials are known that have the infrared absorption characteristic. Of these, some are used as a transparent ink for printing the specific mark on banknotes and valuable securities. The transparent ink of the type described is invisible to the human eyes and no one can find the specific mark printed on a region filled in one color. However, the ink absorbs the light involving wavelengths corresponding to the infrared ray. Accordingly, a device can discriminate from the background the specific mark printed on the region appeared as the single-colored region to the human eye.
When the infrared is used as a basis for discriminating a specific stamp, an erroneous detection may be made due to the presence of some infrared absorbing materials on the back of the original. More specifically, the infrared ray reaches the deep inside of a paper as well as being reflected from the face of the paper because it involves wavelengths longer than those of visible light. A portion of the infrared ray reached to the deep inside is reflected therefrom in an amount depending on the infrared absorbing materials, if any, present there. Carbon black, which is often contained in black inks and pigments for printing, is one of the infrared absorbing materials. Thus, if the carbon black is present on the back of the original, the infrared ray reached to there is absorbed by this carbon black. As a result, there is a disadvantage of erroneously detecting the infrared absorbing materials on the back of the original.
The method relying upon the detection of infrared absorbing material has another disadvantage. The apparatus is so controlled that it copies the infrared-absorbing specific mark printed on the banknotes or valuable securities in a somewhat modified form (by painting all over the paper and so on). Alternatively, the apparatus may interrupt the printing operation when it detects the presence of the infrared absorbing materials. As mentioned above, the infrared absorbing materials are used for printing various patterns on papers other than banknotes and valuable securities. Such papers may be duplicated for justified or authorized purpose. For example, a receipt with a revenue stamp on it is sometimes required to be copied. If the paper to be copied has a certain mark printed on it with the ink containing the infrared absorbing materials, the mark may be lost from the resultant product due to detection of the infrared absorption. In other words, the erroneous detection of the infrared absorbing materials even results in unnecessary loss of important data.
Accordingly, an object of the present invention is to overcome the above mentioned conventional problems.
More particularly, the present invention is directed to provide an image processing apparatus and a method of forming patterns applicable thereto, with which a specific original can be discriminated from others with a high accuracy.
To achieve the above-mentioned objects, according to one aspect the present invention provides an image processing apparatus that includes first judgment means for judging whether image data includes data corresponding to image information that is difficult for human eyes to perceive, second judgment means for judging whether the image data includes data corresponding to line information arranged such that the line information overlaps image information that is difficult for human eyes to perceive, and discrimination means for discriminating whether or not the image data corresponds to a specific image, based on a judgment result of the first judgment means and a judgment result of the second judgment means.
According to another aspect, the present invention provides an image processing apparatus for detecting whether an image includes a pattern having concentric circles in which information that is difficult for human eyes to perceive is arranged along arcs of at least one of the circles. The apparatus comprises extraction means for extracting, from image data corresponding to an image, a data string that contains data corresponding to image information that continues in a predetermined direction on the image and represents the pattern, and comparison means for comparing a group of one or more data strings extracted by the extraction means with a predetermined data group.
According to still another aspect, the present invention provides an image processing method that includes a first judging step of judging whether image data includes data corresponding to image information that is difficult for human eyes to perceive, a second judging step of judging whether the image data includes data corresponding to line information arranged such that the line information overlaps image information that is difficult for human eyes to perceive, and a discrimination step of discriminating whether or not the image data corresponds to a specific image, based on a judgment result of the first judging step and a judgment result of the second judging step.
According to yet another aspect, the present invention provides an image processing method for detecting whether an image includes a pattern having concentric circles in which information that is difficult for human eyes to perceive is arranged along arcs of at least one of the circles. The method comprises the steps of extracting, from image data corresponding to an image, a data string that contains data corresponding to image information that continues in a predetermined direction on the image and represents the pattern, and comparing a group of one or more data strings extracted in the extraction step with a predetermined data group.